Evolution of the pore structure in coal subjected to freeze−thaw using liquid nitrogen to enhance coalbed methane extraction

Qin, Lei; Zhai, Cheng; Xu, Jizhao; Liu, Shimin; Zhong, Chao; Yu, Guoqing

doi:10.1016/j.petrol.2018.12.037

Cited by 101 publications

(33 citation statements)

References 31 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…For example, the coal permeability increased by 48.89%-93.55% after LN 2 cooling treatment, and the compressive strength of cool-treated coal specimens decreased by 16.18%-33.74% compared with intact specimens [4]. Under laboratory conditions, Qin et al [5,10] studied the effect of LN 2 freezing on pores and fracture structures in coal. After LN 2 freezing-thaw cycles, they found that the coal specimens' elastic moduli, uniaxial compressive strengths (UCSs) and longitudinal wave velocities dropped while the porosities and Poisson's ratios increased.…”

Section: Introductionmentioning

confidence: 99%

“…Scanning electron microscope (SEM) and computer tomography (CT) scanning technologies are effective means to investigate the growth and expansion of cracks in geological materials under thermal treatments [42,43]. Cai et al and Qin et al studied the crack propagation in coal using SEM tests and found that LN 2 freezing stretched and increased the number of cracks, and accordingly improved the initial damage degree of the coal [5,[8][9][10]. The change in coal pore structure under increasing temperatures was investigated using SEM technology [44][45][46][47].…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Microcrack evolution and permeability enhancement due to thermal shocks in coal

Zhang

Wang

et al. 2020

PLoS ONE

View full text Add to dashboard Cite

To understand the effects of thermal shock on microcrack propagation and permeability in coal, thermal shock tests were conducted on coal specimens by using a constant temperature drying oven (105˚C) and a SLX program controlled cryogenic tank. The growth and propagation of microcracks were measured with computer tomography (CT) scanning and scanning electron microscope (SEM) tests. Results showed that thermal shocks improved the permeability of coal significantly. Notably, the permeability of coal after thermal shocks increased from 211.31% to 368.99% and was positively correlated with temperature difference. CT scanning images revealed that thermal shocks increased the crack number, crack volume and crack width as well as smoothened and widened the gas flow paths, thereby enhancing coal permeability. Moreover, SEM images showed that heating-cooling shocks created more new microcracks, forming more complex crack propagation paths and better connectivity among microcracks in coal compared to cooling shocks. We proposed a crack propagation criterion for coal to explain the mechanism of crack failure and propagation during thermal shocks. Our experiment results and theoretical analysis indicate that the heating-cooling shock is more effective in damaging and breaking coal than the cooling shock. Thus, it can be used as an alternative approach to enhance coal permeability in the production of coalbed methane (CBM).

show abstract

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Microcrack evolution and permeability enhancement due to thermal shocks in coal

Zhang

Wang

et al. 2020

PLoS ONE

View full text Add to dashboard Cite

show abstract

“…2,10,11 Much exploratory research over the past 100 years has probed this catastrophic phenomenon to obtain an improved understanding of the causative mechanisms and better mitigate outbursts. 6,[12][13][14][15][16][17][18] However, few of the proposed mechanisms can be successfully applied to explain, predict, and prevent outbursts. Due to the unique characteristics of these destructive, short duration, and high-intensity events, outbursts are both unpredictable in space and time.…”

Section: Introductionmentioning

confidence: 99%

Experimental investigation on dynamic strength and energy dissipation characteristics of gas outburst‐prone coal

Fan

Elsworth

et al. 2019

Energy Science & Engineering

110

View full text Add to dashboard Cite

We report laboratory experiments to investigate the dynamic failure characteristics of outburst‐prone coal using a split Hopkinson pressure bar (SHPB). For comparison, two groups of experiments are completed on contrasting coals—the first outburst‐prone and the second outburst‐resistant. The dynamic mechanical properties, failure processes, and energy dissipation of both outburst‐prone and outburst‐resistant coals are comparatively analyzed according to the obtained dynamic compressive and tensile stress‐strain curves. Results show that the dynamic stress‐strain response of both outburst‐prone and outburst‐resistant coal specimens comprises stages of compression, linear elastic deformation, then microfracture evolution, followed by unstable fracture propagation culminating in rapid unloading. The mechanical properties of both outburst‐prone and outburst‐resistant coal specimens exhibit similar features: The uniaxial compressive strength and indirect tensile strength increase linearly with the applied strain rate, and the peak strain increases nonlinearly with the strain rate, whereas the elastic modulus does not exhibit any clear strain rate dependency. Differences in the dynamic failure characteristics between outburst‐prone and outburst‐resistant coals also exist. The hardening effect of strain rate on outburst‐prone coal is more apparent than on outburst‐resistant coal, which is reflected in the dynamic increase factor at the same strain rate. However, the dynamic strength of outburst‐prone coals is still lower than that of outburst‐resistant coals due to its low quasi‐static strength. The dissipated energy of outburst‐prone coal is smaller than that of outburst‐resistant coal. Therefore, the outburst‐prone coal, characterized by low strength, high deformability, and small energy dissipation when dynamically loaded to failure, is more favorably disposed to the triggering and propagation of gas outbursts.

show abstract

“…LN2 boiling point is at -196 °C at atmospheric pressure, and such vaporization generates the latent heat of 5.56 kJ/mol, that in turn result in an expansion of this gas to 696 times in the form of gas at 21 °C. Moreover, in water-bearing coals, the freezing of water provides another source of energy to fracture the rock (Qin et al 2018). Therefore, the feasibility and efficiency of LN2 fracturing has been the matter or research recently.…”

Section: Introductionmentioning

confidence: 99%

Coal fracturing through liquid nitrogen treatment: a micro-computed tomography study

et al. 2020

View full text Add to dashboard Cite

Low permeability of coal has been a constant obstacle to economic production from coalbed methane reservoirs, and liquid nitrogen (LN2) treatment has been investigated as one approach to address this issue. This study examined LN2 fracturing of a bituminous coal at pore-scale through 3D X-ray micro-computed tomography. For this purpose, a cylindrical sample was immersed into LN2 for 60 min. The micro-CT results clearly showed that the rapid freezing of the coal with LN2 generated fracture planes with large apertures originating from the pre-existing cleats in the rock. This treatment also connected original cleats with originally isolated pores and micro-cleats, thereby increasing pore network connectivity. Moreover, scanning electron microscopy highlighted the appearance of continuous wide conductive fractures with a maximum opening size of 9 µm. Furthermore, a nano-indentation technique was used to test the effect of LN2 on coal mechanical properties. The indentation moduli decreased by up to 14%, which was attributed to the increase in the cracked rock compressibility, showing considerable fracturing efficiency of the LN2 treatment. Through in-situ microscopic visualisation and surface investigation, this study quantified the pore structure and connectivity evolution of the rock based on the morphological alteration, and demonstrated the promising effect of LN2 freezing on fracturing of bituminous coals, thus aiding coalbed methane production. The significance of this study was investigating the mechanisms associated with and the efficiency of LN2 treatment of a coal rock in a 3D analysis inside the rock.

show abstract

Evolution of the pore structure in coal subjected to freeze−thaw using liquid nitrogen to enhance coalbed methane extraction

Cited by 101 publications

References 31 publications

Microcrack evolution and permeability enhancement due to thermal shocks in coal

Microcrack evolution and permeability enhancement due to thermal shocks in coal

Experimental investigation on dynamic strength and energy dissipation characteristics of gas outburst‐prone coal

Coal fracturing through liquid nitrogen treatment: a micro-computed tomography study

Contact Info

Product

Resources

About